The sclera is the fibrous elastic coat surrounding the eyeball that provides the structural support and flexibility critical for focusing an image on the retina. Despite its importance in optic development and disease, the molecular mechanisms of sclera development and degeneration are poorly understood. This proposal will fill this gap by capitalizing on novel opportunities for studying sclera development and degeneration in the teleost Astyanax mexicanus, a single species consisting of eyed surface (surface fish) and blind cave (cavefish) forms. In this species, eye tissue manipulation methods, genomic tools, and - most importantly - the existence of a powerful genetic approach, are available. Eye primordia are initially formed in cavefish but subsequently arrest and degenerate. The first cavefish tissue to degenerate is the lens, which subsequently affects development of other optic tissues including the sclera. Transplantation of a surface fish embryonic lens into a cavefish optic cup restores the normal sclera phenotype, showing that the lens functions in sclera development. Other eye tissues, namely the retinal pigment epithelium (RPE) and cranial neural crest (CNC), may also control aspects of sclera development. The overall goal of this project is to determine the molecular mechanisms of sclera development and degeneration. The first specific aim is to investigate the roles of the lens, RPE, and CNC as organizers of sclera development. This aim will use a combination of physical and genetic manipulations to reveal the contributions of these eye tissues in organizing the developing sclera. The second specific aim will identify the genes expressed in the lens, RPE, CNC, and/or the sclera itself that mediate normal and abnormal sclera development. These genes will be filtered for specifically and reduced to a manageable number by mapping to a set of specific genomic regions (QTL) responsible for the abnormal sclera phenotype. The third specific aim will determine the function of the sclera related genes by manipulating their expression in surface fish and cavefish and determining the effects on sclera development. The fourth specific aim will identify the mutations in genes responsible for sclera defects. This study is designed to reveal the mechanisms, genes, and mutations responsible for visual decay through effects on development of the sclera.